There is a need in the electronic arts, especially semiconductor arts, to etch cavities of various depths into substrates. Etched cavities are often used to provide thin diaphragms in connection with micro-electro-mechanical system (“MEMS”) elements. For example and not intended to be limiting, by placing a deflection sensor on such a thin diaphragm, a pressure sensor MEMS element can be created. It is common to have other electronic and/or optical devices, integrated circuits (ICs), and various other sensors or actuators associated with MEMS elements. As used herein, the terms “MEMS”, “MEMS element” and “MEMS device” are intended to include such other devices, ICs, sensors and actuators.